For drilling a wellbore from an onshore or offshore drilling platform, for example for an oil well or natural gas well, a plurality of drillpipes are connected together in succession to form a drillstring carrying the drilling bit progressively deeper into the wellbore being drilled. The individual drillpipe sections or strands are screwed together via screw threadings at their ends, sometimes additionally using threaded couplings. Thus, during the drilling operation, it is necessary to manipulate drillpipe sections into place, and to manipulate suitable screwing tools and clamping tools for screwing the screw threadings of the drillpipes to one another or to couplings interposed between successive drillpipes. Also, the screwed or threaded connections must be tightened to a respective defined proper torque. Because the drillpipes, couplings and other components are sizeable and heavy, these operations are carried out with correspondingly heavy and sizeable clamping tools, screwing tools, and the like generally known in the field of well drilling.
In view of the above, it is also known to use power-operated manipulators to carry and manipulate the tools for performing the abovementioned operations. The power-operated manipulator must be adapted to carry the respective suitable tool to a proper location with respect to the wellbore, and to enable a height adjustment of the tool relative to the top end of the drillstring in order to accommodate various heights of the top end of the last added strand or pipe section of the drillstring. Once properly positioned with respect to the drillstring, i.e. the drillpipe section or the coupling or the like, the tools carry out the necessary operations mentioned above.
It is known to suspend tools of this type from a cable crane, and to move the crane so as to move the tool into the proper working area. Thereby the space above the wellbore is drastically limited because the crane and cable equipment must be positioned directly above the wellbore. Furthermore, the entire crane structure takes up relatively much space, especially in the height direction above the wellbore. Another problem with the known cable crane suspension of the drillpipe connecting tools is that the suspension cable does not provide a fixed rigid positioning of the tools, but rather any suspended tool may start swinging or oscillating on the cable. Such an unstable position of the tool makes it difficult to bring the tool into the exactly proper position for carrying out its work.
It has further become known in the art to provide a rail-mounted and rail-guided support arrangement for carrying such tools to the wellbore location. Such rail-guided systems are rather complex, suffer a further disadvantage of being inflexible and not adaptable to various applications, and also encroach on the space around the wellbore due to the guide rails mounted on the drilling platform floor, for example.